The invention relates to fluid supply apparatus for supplying fluid media for use at the internal surface of a tubular workpiece.
In the manufacture of metal pipe, it is often necessary to treat the internal surface of the pipe with a fluid medium; for example, with a jet of air containing sand particles, for sand blasting, or with a jet of air containing finely divided globules of paint, for paint spraying; and so it is necessary to pass the discharge end of a conduit for the fluid medium along a helical path over the internal surface of the pipe so as to direct a jet of the fluid medium onto the internal surface. Similarly, to perform mechanical operations on the internal surface of a tubular workpiece, such as a metal pipe, by means of fluid driven tools such as pneumatic grinding wheels, or to heat the internal surface of the pipe by means of a gaseous medium which is passed over a heater or which is formed by mixing two different gaseous media for combustion in a combustion heater, it is necessary to pass the discharge end of a conduit for the gaseous medium along a helical path over the internal surface of the pipe and into a mechanical tool which is driven by the fluid medium, or into a heater.
In the past, apparatus of this kind has been constructed so that rotation has been effected as a result of the reaction of a tangential component of the fluid medium discharging from the appartus. However, in this case, the speed of rotation was dependent upon the pressure and rate of flow of the fluid medium. Thus, it was not possible to vary the speed of rotation without varying the pressure and rate of flow of the fluid so that it was impossible to maintain this pressure and rate of flow at optimum values.
This deficiency has, to some extent, been overcome by providing the apparatus with a rotatable nozzle and drive means for positively rotating the nozzle at a speed independent of the pressure and rate of flow of the fluid fed to the nozzle. An apparatus such as this is described in U.S. Pat. No. 3,071,107.
However, in apparatus such as this, the rotatable nozzle is fed from a single rotatable supply pipe so that material in addition to a first fluid fed through the rotatable supply pipe; for example, sand or paint particles entrained in a stream of air or a mixture of oxygen and acetylene or oxygen and some other combustible gas; must be mixed prior to entry to the rotatable supply pipe and this can cause difficulty.
For example, where a combustible gaseous mixture is to be burned in a heater, prior mixing of the components of the combustible mixture results in a safety hazard which could be overcome by feeding the two gaseous components separately to the burner. Similarly, entrainment of liquid particles in a jet of a gaseous medium; for example, in spray painting where globules of paint are suspended in a jet of air; may be effected more efficiently if the liquid and the gaseous media are mixed immediately prior to their application to the internal surface of the tubular workpiece. One way of avoiding this pre-mixing in the application of a liquid spray to the internal surface of a tubular workpiece is to pressurize the liquid so that "atomization" is effected without the use of an air jet, as in "airless spraying". Unfortunately, this "airless spraying" technique involves the disadvantage that when starting and stopping, while the pressure of the liquid is less than that required to effect "atomization" of the liquid, the liquid runs from the nozzle in an uncontrolled manner. It is therefore necessary to provide the nozzle with valve means to prevent the escape of liquid at a pressure less than that required to convert the liquid into a spray. This is most effectively done by means of a fluid operated mechanism for controlling the valve, but this mechanism is most effectively controlled by means of a separate fluid supply line. Similar considerations apply in respect of other fluid driven tools, in that control may be conveniently effected by means of fluid responsive means requiring an additional fluid supply line. This also applies when a synthetic resin such as epoxy resin or a polyurethane is to be applied to the internal surface of a tubular workpiece, together with an activator or hardener. If these constituents are mixed prior to application, there is a chance that the resin will solidify within the apparatus, particularly during temporary stoppages of the apparatus. In cases such as this, it is preferable to provide the constituents in the form of pressurised liquids which are fed independently to separate nozzles where they are airlessly sprayed into a common atomized jet where particles of the constituents combine and react on settling on the internal surface of the tubular workpiece.
One form of apparatus suitable for applying two or more fluid constituents to the internal surface of a tubular workpiece is described in U.S. Pat. No. 1,839,891. In apparatus such as this, drive means are provided for rotating an assembly of coaxially nested tubular members of equal length which are connected at their ends for rotation in unison. A first fluid medium is fed axially through the inner tubular member and different fluids are fed to annular cross-section spaces between radially adjacent tubular members through radial pipes which extend from openings in the surface of the outer tubular member. These openings are arranged for rotation in chambers enclosed by sleeves disposed around the outer tubular member. These sleeves are respectively provided with seals at their opposite ends for engagement with the outer tubular member on opposite sides of the chambers around the openings of the radial pipes. The outlets from the inner tubular member and from annular cross-section spaces between radially adjacent tubular members are communicatively connected to radially extending pipes so that, on rotation of the device, fluid material discharging from the open ends of these radial pipes is applied to the internal surface of a tubular workpiece. In apparatus such as this, each annular cross-section space disposed between radially adjacent tubular members extends throughout the whole length of the assembly of coaxially nested tubular members and so there are relatively large volumes of fluids in each of these spaces which remain stagnant and which cannot be flushed from the apparatus by cleaning fluids passed through the apparatus, as is necessary when dealing with liquids such as paint which can solidify if the apparatus is allowed to stand without operating. These pockets of stagnant fluid also constitute a safety hazard when formed of inflammable gas or vapour, because of the possibility of leakage.
Another disadvantage of the hereinbefore described apparatus is that sealing of the annular cross-section spaces between radially adjacent coaxially nested tubular members is effected by the seals between the outer sleeves and the outer tubular member so that the leakage can occur around the whole circumference of this, the largest tubular member in the assembly of coaxially nested tubular members.